Valuable chemical compounds such as fragrances have been encapsulated for protection, storage, and controlled release. Encapsulation refers to processes whereby an active ingredient is placed into a stabilized form. The release of active ingredient from the protected form may be rapid (such as by crushing, or by ingestion), or gradual (such as by dissolution, diffusion, or bio-degradation). In this manner it is possible to maximize the effectiveness of the active ingredient by ensuring that it is released at the proper time.
The term “microcapsule” has been used to describe small particles or beads having a size ranging from less than one micron to several millimeters, which may contain a wide variety of active ingredients (Thies (1994) Today's Chemist November p. 40; Goodwin (1974) Chemtech Magazine October p 623-26). Microcapsules refer to two broad groups: (1) “Aggregate” microcapsules having the active ingredient dispersed throughout a continuous matrix. The matrix may be a solid polymer or a gel swollen with solvent. In the case where the gel is swollen with water, the term “hydrogel” is applied. Hydrogel encapsulation systems of this type have been described and are generally based on cross-linked forms of water-soluble polymers such as alginate, gelatin, pectin, agar, gellan, or starch (Sanderson, et al. (1989) Cereal Foods World 34(12):993-998). (2) “Mononuclear” microcapsules, on the other hand, are composed of materials that show a true “shell-core” morphology. These are similar to an egg in that they have a solid shell or flexible membrane surrounding a core which may be a liquid, a solid, or even a gel.
U.S. Pat. No. 3,808,686 discloses the preparation of an organic solution of a water-insoluble, organic solvent soluble hydrophilic polymer for application to denture prostheses to eliminate denture breath. However, this preparation is strictly a matrix-based system, wherein the active ingredient is entrapped by physical absorption, which is not suitable for consumer applications such as personal care and fabric.
U.S. Pat. No. 3,660,563 discloses water-soluble polymers containing fragrances, drugs, soaps, etc. entrapped therein. However, this is a particle-based system that would not be able to retain fragrance oil in a base.
EP 1146057 discloses cross-linked polymeric nanoparticles for carrying skin care ingredients, e.g., fragrances, essential oils, etc. and food ingredients. However, this is, as claimed, a particle approach, wherein the fragrance is loaded in situ and the particle size is in the nanometer range, which would have poor stability in personal care and fabric application.
US 2002/0050659 teaches hydrocapsules for encapsulating a liquid, e.g., a solution, fluid, slurry, paste or suspension. However, the hydrocapsules of this document are coextruded and have low loading capacity and stability.
US 2012/0058929 teaches a microcapsule carrier system for fragrances, wherein the core of the microcapsule is composed of a fragrance and the shell is obtained by polymerizing one or more C1-C24 alkyl esters of acrylic acid and/or methacrylic acid; and methyl methacrylate (MMA), 1,4-butanediol diacrylate (BDA), pentaerthrityl triacrylate (PETIA) and/or ethylene glycol dimethacrylate (EDGMA). However, the microcapsules of this reference are small, have poor stability, and have a high level of polymer wall material compared to core material.